DE69508023T2 - Initial charge - Google Patents

Abstract

A primer composition which does not result in the deposit of toxic substances when detonated, said primer comprising a dinitrobenzofuroxan salt, a diazinate or a dinitrophenylazide salt together with an oxidizer and a relatively high proportion of friction agent. A typical set of components are KDNBF with KNO3 and ground glass.

Description

The invention relates to primers (initial charges) for use in impact fuses for ammunition and in particular, but not exclusively, to primers for rim-ignition ammunition.

Until now, such compositions have included two sensitive primary explosives together with oxidizers, friction agents and propellant. The most commonly used primary explosive is lead styphnate, which is always accompanied by a second primary explosive, tetrazene, which is essential to give the composition sufficient sensitivity to impact and a reproducible response. The most commonly used oxidizer is barium nitrate and antimony sulfide is often used as a propellant.

These primers typically contain elements such as lead, antimony and barium, which are now considered highly toxic. Such elements pose a potential health hazard, particularly within enclosed shooting ranges, where they accumulate in the atmosphere and on surfaces. In recent years, there has been a trend towards so-called non-toxic primers.

These non-toxic primers contain diazodinitrophenol (DDNP) together with a sensitizing explosive such as tetrazene. Examples of such non-toxic primers can be found in EP Patent No. 0 440 873 (Blount Inc.), US Patent No. 4 674 409 (Olin Corporation) and others. Typically, the completeness of ignition in these compositions was In particular, these requirements are inadequate for rim-ignition ammunition. Under the relatively unconstrained conditions encountered in loading rim-ignition ammunition, complete and rapid explosion of the primer charge does not easily occur.

Furthermore, the requirement of a second primary explosive, such as tetrazene, acting as a sensitizer in the primer, introduces additional mixing and manufacturing requirements. The inherent color of DDNP also makes it difficult to see within a brass ammunition casing.

It would be advantageous to provide a non-toxic composition comprising a single explosive together with a friction agent, oxidizer and binder. Furthermore, significant advantages would be gained if the composition had a color that was easily distinguishable from a brass coating. The explosive should not contain any toxic elements to be non-toxic. For example, it could be a salt of a non-toxic element. Known non-toxic explosives formed from non-toxic elements are metal salts of dinitrobenzofuroxan including the potassium and sodium salts (KDNBF and NaDNBF).

It is imperative that the rimfire ammunition be suitably sensitive to provide consistent and reliable ignition. Typically, primer-filled cartridge cases are tested by dropping a known weight from a known height onto a firing pin resting against the primer-filled rim of the case. It is thus detected that when the weight is dropped onto the pin, the rim is depressed and the primer explodes. The mean firing height is the height from which the weight must be dropped to explode 50% of the sample charges. Acceptable firing heights vary for different types of ammunition and to a large extent it is important It is better that the primer is consistent in its response to impact than that it is too sensitive.

Total height of fire is the height from which the weight must be dropped to explode all of the charges (priming charges) in a sample (typically 50 charges). Typically, total height of fire using a 2 oz (57 g) weight and a chisel bolt found in many target weapons is between 9 to 11" (229 - 279 mm), which is acceptable for rimfire target ammunition.

The primer must explode fully and quickly when the rim of the cartridge is suitably struck. As shown in EP 0 529 230 (Blount Inc.) and US Patent No. 4 674 409 (Olin Corporation), a pack may be placed above the primer in the rim of such ammunition to spatially confine the primer at least initially and to ensure complete combustion so as to increase the effect of ignition on the propellant. Such confinement requires the introduction of combustible materials such as a layer of compressed propellant into the cartridge which can disrupt the consistency of the propulsive impulse imparted to the bullet and render such ammunition unsuitable for competitive shooting.

Unfortunately, previous investigations, for example in EP 0 580 486 (NCS Pyrotechnie et Technologies), have shown that a combination of two primary explosives is only effective if KDNBF is used. Tetrazene must be used as a sensitizer. It has thus far been found that a charge made from a single explosive is either too uneven or too insensitive.

US-A-5 167 736 discloses a non-toxic primer composition for use in an impact detonator (impact charge) which basically comprises diazodinitrophenol and boron. The composition can also contain an oxidizer, a propellant and tetrazene as a secondary explosive.

GB-A-1 210 604 discloses a process for producing the barium salt of dinitrobenzofuroxan from the sodium salt, the barium salt being suitable as an initiator charge explosive. Additional sensitizing explosives increase manufacturing complexity and costs. Furthermore, the sensitizing explosive tetrazene is unstable and can deteriorate over time, thus affecting the performance of the charge (the detonator).

Typically, primers are mixed as a paste with a little water. This paste is then distributed and packed into holes provided in a charge plate. The cylinder of primer packed into each hole represents the amount of charge for each case or percussion cap.

The paste is ejected from the charge plate as a pellet into each case or cap by means of a suitable rod or pin. This provides a cylindrically shaped volume of primer paste at the bottom of each case. In rim-ignited ammunition it is necessary to pack this primer evenly into the rim at the base of the case. A common technique is to rotate a tool inserted into the case so that the charge is packed into the rim. The primer is effectively squeezed or pumped into the rim.

Once the primer is in the rim, each case is dried either forcibly or naturally to expel any residual water within the composition, leaving a dry fillet of sensitive composition around the base of the case. If required, a small amount of a water-soluble adhesive or binder may be included in the mix to ensure the integrity of the fillet. The table shows Dry matter contents are given for comparison between compositions.

According to the invention there is provided a non-toxic primer composition suitable for use in rimfire ammunition comprising as a dry weight percentage a dinitrobenzofuroxan salt as the only primary explosive in the range of 25 to less than 50%, an oxidizer in the range of 10 to 40% and a friction agent in the range of 10 to 40%, the composition not comprising tetracene.

In a particular embodiment of the invention there is provided a non-toxic primer comprising a dinitrobenzofuroxan salt in the range of 40 to 45% together with an oxidizer in the range of 17 to 35% and boron and/or glass particles in the range of 15 to 40% expressed as a dry weight percentage. When boron particles/crystals are used it may be preferable to mix them in amounts in the range of 20 to 35% or 30 to 35% depending on the coarseness of the boron particles.

The oxidizing agent can be, for example, potassium nitrate, manganese dioxide or zinc peroxide.

When boron particles are used as an abrasive, it is desirable to use particles of a coarse fraction as they are more effective in increasing the sensitivity of the initial charge compound. Typical ranges of such boron particles are 100 to 150 µm or 75 to 100 µm or a combination of such ranges.

Boron particles may comprise 15 to 40% of the composition. A non-toxic cargo propellant may be incorporated, and makes up 2 to 20% of the dry weight. A binder may comprise 0.5 to 5% by weight.

Preferably, the abrasive is ground glass or boron particles.

Preferably, the propellant used is aluminum powder, calcium silicide, sulfur, sieved bullet propellant powder or a similar material.

A desired composition of the charge (initial charge) consists of 45% dinitrobenzofuroxan salt, 15% oxidizer, 35% friction agent and a balance of fuel and binder. Alternatively, 40% KDNBF, 25% oxidizer, 35% friction agent can be used.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying Table 1 which sets out various primers and the results.

In the column headings of Table 1, the impact sensitivity is given by the mean height of fire H, the standard deviation S and the number of non-igniting cases among 50 samples tested at a drop height of 9 inches (229 mm), all tests being conducted in a steel test case equipped with a chisel bolt and using a 2 oz (57 g) weight. It can be seen that a low number of misfires at 9 inches (229 mm) indicates good sensitivity.

Taking into account Table 1, Composition A shows the potassium salt of dinitrobenzofuroxan mixed with potassium nitrate as oxidizer, tetrazene as secondary explosive or sensitizer and glass powder as friction agent. The mean fire height (H) and standard deviation (S) of fire height are both acceptable. This Composition A corresponds to EP 0 580 486 (NCS), according to which prior art teaching a secondary explosive or sensitizer, tetra zen, is required to ensure uniform fire height behavior for dinitrobenzofuroxan primers.

Compositions B and C are known lead styphnate primers, Composition B being a common "spinning charge" composition for rimfire ammunition. The styphnate is mixed with barium nitrate, tetrazene, dye and lead hypophosphite. The results are acceptable in terms of height of fire (H) and better than Composition A in terms of consistency as shown by the standard deviation (S) of height of fire. Similarly, Composition C was prepared according to the so-called ELEYPRIME process of Eley Limited (UK Patent Nos. 1 569 874 and 2 075 OOOB) and was used in this example as a spinning charge mixture which produced good heights of fire and consistency of height of fire behavior. However, these compositions still require tetrazene as a sensitizer and thus have a complicated two explosive composition. The dye is added to ensure that the charge is visible in the case upon visual inspection.

The compositions D - J and L - U are single explosive charges (initial charges) according to the invention.

Composition D comprised 40% potassium dinitrobenzofuroxan (KNDBF) with 25% potassium nitrate as oxidizer and 35% ground glass as abrasive. The mean height of fire (H) is good and the consistency as shown by the standard deviation (S) of height of fire is outstanding. The ballistic performance may be poor in some cases possibly due to an effective reduction of the explosive content from 45% (40% KDNBF, 5% tetrazene) in Composition A to only 40% KDNBF.

Composition E has a similar explosive content to composition D, but 5% aluminum powder was used as a propellant together with 2% dextrin as a binder at the expense of of the oxidizer content. The mean fire height (H) and standard deviation (S) remained good. However, similar problems as with composition D may occur in terms of behavior due to the explosive content.

Composition F had 45% KDNBF with similar levels of KN03 oxidizer and glass friction agent as composition E, but no fuel. The mean fire height (H) is acceptable, but the consistency shown by the standard deviation (S) is reduced; however, this was probably due to packing errors in the rim. Furthermore, one misfire was found to occur in a sample of 50 cases tested at 9" (229 mm) drop height, but this is acceptable within the overall fire criteria of 9 to 11" (229 to 279 mm).

Composition G had the same level of the explosive KDNBF but reduced the level of the oxidizer KN03 to accommodate 5% sulfur as the fuel. The average height of fire (H) is slightly improved compared to composition F and the consistency is much better. However, there were two misfires in a sample batch of 50 sample cases at a drop height of 9" (229 mm), but again this is acceptable within the desired overall fire criteria.

During the process of filling the charge plate, it was found that Composition G had a tendency to disintegrate or fractionate possibly due to the effect of the water repellent sulfur. However, there was no obvious benefit or detrimental effect from the addition of sulfur as compared to aluminum powder.

Composition H is similar to composition E, using aluminum powder as fuel, except that the content of the explosive KDNBF was increased by 5%. The results The results show a slightly higher mean height of fire (H) but better consistency. However, the ballistic behavior was very good and comparable to current high-quality rimfire ammunition.

The cases loaded with composition H (.22LR) were loaded with 72 mg of single base propellant, filled with bullets and provided with a guide groove and lubricated in the usual way to produce standard velocity .22 caliber ammunition. The recorded pressures and muzzle velocities were on average 106.6 MPa (standard deviation 3.4 MPa) (14740 psi (standard deviation 490 psi)) and 325 m (1067 feet) per second (standard deviation 2.2 (7.1)). The diameters of 10-shot groups at 50 meters were 19.1, 11.3, 16.2, 13.1 and 12.4 mm. The diameters of the groups at 91.4 m (100 yds) were 36.1, 22.2, 28.7, 32.7 and 27.9 mm. Composition I contained consistent, high explosive KDNBF, but the proportions of oxidizer KN03 and ground glass were inversely proportional to composition H. The results are poor in both average fire height (H) and consistency. Thus, the friction agent (glass) is important in providing a practical charge of dinitrobenzofuroxan salts. A high glass content is important in single explosive charges of DNBF salts.

Composition J had approximately equal levels of KNO3 oxidizer and ground glass friction agent compared to previous compositions. Composition J has approximately mid-range levels and gives approximately mid-range results. However, when tested, the sample showed a surprisingly low number of misfires when tested on 50 cases at 9" (229 mm) drop height.

Composition K had an increased content of KDNBF at 50%, while the content of the oxidizer KNO3 was reduced to 10%. The contents of fuel (aluminium powder), glass and binder were similar to previous compositions. The mean fire height (H) and standard deviation (S) are acceptable, but there appears to be a reduction in performance compared to an improvement expected from an increased explosive content over previous primers. Again, this is most likely due to the distribution of ingredients.

Composition L had 45% KDNBF explosive and only 10% oxidizer (KNO3) but an increased 40% friction agent (glass). The average height of fire is good, but the consistency is outstanding. Furthermore, no misfires were observed in a test of 50 cases at 9" (229 mm) drop.

In composition M, aluminum powder was replaced by 5% sieved bullet propellant as the fuel/gas producer. This has no detrimental effect on the mean fire height (H) and standard deviation (S). Similarly, in composition N, where calcium silicide is used as the fuel, the results were consistent with the previous performance.

Composition P is similar to composition F except that instead of potassium nitrate the oxidizer is finely divided manganese dioxide. The results of mean height of fire (H) and consistency are satisfactory. Similarly, composition Q has zinc peroxide as the oxidizer and the results are good. However, both compositions P and Q were found to give rather weak results and therefore, although they may be suitable as blanks, they may not have sufficient explosive power for rimfire ball ammunition.

In composition R, crystalline boron has been shown to be an extremely effective abrasive and gives phenomenal sensitivity. It may turn out to be too sensitive for commercial use.

The results of composition S with mixed crystalline boron with a grit size of 100 to 150 µm confirms the effectiveness of crystalline boron.

The results of composition T with mixed crystalline boron with a grit size of 75 to 100 µm show that using a smaller grit size of crystalline boron reduces the sensitivity.

According to the invention it has also been found that a separate charge propellant is not always necessary. In this case boron behaves in some respects as a propellant as well as a friction agent, but it is not always necessary for a charge propellant as such to be present in the ignition composition.

The results for composition U show that manganese dioxide with coarser grit size (100 to 150 µm) can be used satisfactorily in a rim ignition charge, apparently by combining the action as an oxidizer with some frictional effect.

Composition V is a simple mixture without binder or separate fuel and shows very good sensitivity and good ballistics.

Composition W is included in Table 1 as an example of a relatively toxic load which otherwise has satisfactory results.

As an alternative to using KDNBF or a dinitrobenzofuroxan salt, a dinitrophenyl azide salt or a diazinate could be used as the primary explosive.

In Table 1, in the column marked "Other", the indices, additions or changes identify the following:

1 = Lead hypophosphite

2 = sieved ball powder

3 = Calcium silicide

4 = Manganese dioxide

5 = zinc peroxide

6 = Bor

7 = Sulfur

From the results shown in Table 1, it is clear that the level of the abrasive is the principal determining factor in performance. The oxidizer can be changed without too much deleterious effect or improvement in results, while the level of the abrasive affects performance. It can be assumed that many grit-like materials including sand, minerals, carbides, calcium silicide, ground coke and other abrasive grit could be used together with ground glass as has been shown. The table shows some results regarding misfires at 9" (229 mm) drop height. As stated above, it is generally accepted that there must be a total height of fire of between 9" (229 mm) and 11" (279 mm). If there are less than 2 misfires at 9" (229 mm), it can be safely assumed that there are no or only rare misfires at 11" (279 mm), an acceptable total height of fire for general target ammunition. From the misfire results it is clear that compositions I and J, ie those with lower content of the friction agent (glass), show poorer results. Such results emphasize the need for a high content of friction agent to create an ignition composition according to the invention.

Some current lead styphnate primers used in high quality .22 RF target ammunition use on the order of 36 mg of primer charge in each case along with 25% glass. This is due to the use of a single-drive type packing technique rather than a rotary charge. Thus the glass content is 9 mg, whereas a single explosive primer according to the invention would have about 18 mg per case with 35% or 6 mg of glass.

Typically, KDNBF may have a particle size of about 10 µm, the oxidizer may have a size of about 100 to 150 µm, and the glass may have a size of about 75 to 150 µm.

Acceptable composition ranges for potential primers are (% dry weight):

KDNBF 25-55%, preferably 45%

Oxidizing agent 10-40%, preferably 15%

Abrasive 10-45%, preferably 35%

Fuel 3-15%, preferably 5%

Binder 0.2-2%

The preferred DNBF salt is potassium dinitrobenzofuroxan with potassium nitrate as the oxidizing agent.

It is understandable that dinitrobenzofuroxan can be produced in-situ within the case or casing, thus reducing the risk of explosion when loading the case. Table 1

Claims (12)

1. A non-toxic primer composition suitable for use in rimfire ammunition comprising, in dry weight percentages, 25 to less than 50% dinitrobenzofuroxan salt as the only primary explosive, 10 to 40% oxidizer and 10 to 40% friction agent, the composition not containing tetrazene. 2. Ignition composition according to claim 1, comprising - each expressed as a dry weight percent - 40 to 45% dinitrobenzofuroxan salt, together with 17 to 35% oxidizing agent and 15 to 40% glass particles as friction agent. 3. Ignition composition according to claim 1, which contains 20 to 35% crystalline boron particles as a friction agent. 4. Ignition composition according to one of the preceding claims, in which potassium nitrate is the oxidizing agent. 5. Ignition composition according to claim 3, in which the size of the boron particles is 75 to 100 microns. 6. Ignition charge according to one of the preceding claims, which contains a non-toxic ignition agent which represents 2 to 20% of the dry weight of the ignition charge. 7. Ignition composition according to one of the preceding claims, which contains a binder representing 0.5 to 5% of the weight of the igniter. 8. Ignition composition for use in rimfire ammunition according to claim 1, comprising 45% dinitrobenzofuroxan salt, 15% oxidizer, 35% friction agent as well as fuel and binder. 9. Ignition composition according to claim 1, comprising 40% potassium dinitrobenzofuroxan, 25% oxidizer and 35% friction agent. 10. Ignition charge according to claim 1, comprising - each stated in dry weight percent - 25 to less than 50% dinitrobenzofuroxan salt, 10 to 40% potassium nitrate as oxidizing agent, 0 to 20% aluminum powder as fuel and 10 to 40% friction agent. 11. Ignition charge according to claim 10, consisting of 40 to less than 50% dinitrobenzofuroxan salt, 15 to 35% potassium nitrate, 15 to 35% glass powder, 0 to 5% aluminum powder and 0 to 2% binder. 12. Ignition composition according to claim 1, comprising - each given in dry weight percent - 25 to less than 50% dinitrobenzofuroxan salt, 10 to 40% potassium nitrate, manganese dioxide or zinc peroxide as oxidizing agent and 10 to 40% friction agent.